Author: Jun Pataleta
MDL-66143 course: Add relativedatesmode course setting
http://git.moodle.org/gw?p=moodle.git;a=commit;h=9d8cdb9ba8eb6602b9b6f587dc2d50ecd3687ed6
http://github.com/moodle/moodle/commit/9d8cdb9ba8eb6602b9b6f587dc2d50ecd3687ed6
+ 3.8 en [relativedatesmode,core]
+ 3.8 en [relativedatesmode_help,core]
+ 3.8 en [relativedatesmode_warning,core]